Deploying Property Checkers

The default Property Checkers introduced in sudoswap V2 can be cloned using the Property Checker Factory at 0x031b216FaBec82310FEa3426b33455609b99AfC1. The contract has two write methods, one for deploying each type of Property Checker.

Both types of default Property Checker conform to the IPropertyChecker.sol interface expected by pair contracts:

interface IPropertyChecker {
    function hasProperties(uint256[] calldata ids, bytes calldata params) external returns(bool);


A RangePropertyChecker can be deployed using the createRangePropertyChecker method. The method's two parameters startInclusive and endInclusive are tokenIds for which all tokenIds in [startInclusive, endInclusive] will be considered valid by the Property Checker.

When interacting with a RangePropertyChecker, the optional bytes calldata parameter on the hasProperties method is not used.


A MerklePropertyChecker can be deployed using the createMerklePropertyChecker method. The method's one parameter is the root of the Merkle tree of all tokenIds which should be considered valid by the Property Checker.

When interacting with a MerklePropertyChecker, the bytes calldata parameter on the hasProperties method is used to pass an array of Merkle proofs for the tokenIds being verified. Individual proofs should be of type bytes32[] and should be encoded together as a single bytes[].

When interacting with a pair that implements a MerklePropertyChecker, traders must have access to Merkle proofs for relevant tokenIds through a frontend interface or otherwise.

Merkle Tree Construction

MerklePropertyChecker implements OpenZeppelin's MerkleProof.sol contract to verify proofs. The hashing function used for both leaf and branch nodes is keccak256(abi.encodePacked()).

To generate a compatible Merkle tree, you can use a JavaScript library like @openzeppelin/merkle-tree. For this specific library, you must adjust the hashing function in standard.ts to match what is provided above.

function standardLeafHash<T extends any[]>(value: T, types: string[]): Bytes {
  return keccak256(hexToBytes(defaultAbiCoder.encode(types, value)));

Security Note

OpenZeppelin advises against constructing Merkle trees with simple hashing functions like keccak256(abi.encodePacked()) due to the risk of second pre-image attacks. However, MerklePropertyChecker is resistant to this type of attack because it is not possible to pass two concatenated keccak256 hashes (totalling 64 bytes in length) as a uint256 tokenId. Not to mention, most NFT contracts do not allow minting of specific tokenIds.